Short pulse generator

ABSTRACT

A spark generator is provided which is reentrant, can deliver all output to a single load while being either balanced or unbalanced to ground, as desired. The structure is operable over a wide frequency and power level range.

D United States Patent 1191 1111 3,798,461

Edson Y Mar. 19, 1974 1 SHORT PULSE GENERATOR 2644.740 7/1958 Schofield313/325 1126.694 l0 l969 H l 75 Inventor: William A. Edson, Los AltosHills, 2 884 6O5 4/1959 Cahf- 3,629,605 12/1971 Nilsson 307/106 [73]Assignee: Stanford Research Institute, Menlo P Cahf' PrimaryExaminer-David Smith, Jr. 22 Filed; N0 21 1972 Attorney, Agent, orFirm--Lindenberg, Freilich &

[21] Appl. No.: 308,483 Wasserman [52] US. Cl 307/106, 3l3/325, 315/3651 1m. 01 H03k 3/00, n031 3/64 [571 ABSTRACT [58] Fleld Search 3 A sparkgenerator is provided which is reentrant, can 315/209, 36, 333/31 C, 31/69, 0 g 6 deliver all output to a single load while being either 7 1 11balanced or unbalanced to ground, as desired. The structure is o er'ableover a wide fre uenc and OWer [56] I References Cited levelrange p q y pUNITED STATES PATENTS 3,454,823 7/1969 Marx et a]. 315/36 8 Claims, 6Drawing Figures PATENTED "AR 1 9 I974 SHEU 2 0F 2 IIIIIIIII/ E OPERATINGPOTENTIAL E OPERATlNG POTENHAL BACKGROUND OF THE INVENTION Thisinvention relates to spark pulse generators and, more particularly, toimprovements in the construction thereof.

Spark pulse generators are circuits comprising inductances, capacitorsand resistors connected in the manner of a filter or transmission line.The capacitors are first charged, then discharged into the inductances.The inductances thereafter discharge into the capacitors. Thus, a numberof cycles or oscillations occur providing pulses which can be applied toa load. Examples of such pulse generators are shown in a patent toSamsel, US. Pat. No. 2,792,508, or in articles by Hellar and Holter, onPages 161-170 of the 1953 Proceedings of the National ElectronicsConference, entitled, A Transmission Line Oscillatory Pulse Generator,or in an article by Weibel in the Review of Scientific Instruments,Pages 173-175, February 1964, entitled, High Power Pulse Generator.

Spark gap generators normally find use in radar, ionosonds and otherapplications, where very short, high power, rf pulses are required.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is theprovision of a simpler and more compact construction fora spark gappulse generator, then has been available heretofore.

Another object of this invention is the provision of a uniqueconstruction for a spark gap pulse generator.

Still another object of this invention is the provision of a spark gappulse generator which is operable over a wide frequency range and can beoperated over a wide power level range.

These and other objects of the invention may be achieved in anarrangement wherein a spark gap pulse generator comprises, in oneembodiment, a pair of spaced parallel discs having centrally positionedopposed protuberances or bosses, which form a spark gap therebetween.The discs have a purality of opposed openings disposed around theirsurfaces out of which tubes extend outwardly. A conductor is threadedthrough the tubes without touching their-walls. A load isattached to theends of the conductor. The tubes and conductors are coaxially related. Avoltage is applied to the discs until a spark occurs across the sparkgap formed between the two opposed bosses. In a second embodiment, apair of opposed spaced drums have opposed bosses therebetween defining aspark gap. A plurality of radialnotches are formed in the periphery ofeach drum. A conductor threads through all of the radial notches of bothdrums without touching the walls and a load is connected to the ends ofthe conductor.

A BRIEF DESCRIPTIONOF THE DRAWINGS FIG. l'is a circuit diagram of anembodiment of the invention employing lumped circuit components.

FIG. 1A is a waveform representative of the load cur rent available withthe structure shown in FIG. 1.

FIG. 2 is a top view of one embodiment of the invention.

FIG. 3 is a side view of the embodiment of the invention as seen in FIG.2.

FIG. 4 is a top view of another embodiment of the invention.

FIG. 5 is a side view of the embodiment of the invention shown in FIG.4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, theremay be seen a circuit diagram of a lumped constant arrangement of thisinvention. A load 10 is represented by a resistor. On either side of theresistor are inductances l2, 14, which are connected in seriestherewith. Each of these inductances has the value l/2L. Connected inseries with the inductance 12 are three other inductances respectively16, 18, 20, which have the value L, or twice that of the inductance 12.Connected in series with the inductance 14 are inductances 22, 24, 26and 28 which have. the value L. The inductance 28 is connected back tothe end of the inductance 20 at the point designated by the letter A.

Between the junction of the inductances 22 and 24, and a bus line 30,there is connected in series a capacitor 32, and an inductance 34.Connected in series between the junction of an inductance 14 and 22 andthe bus 30, is a capacitor 36, and an inductance 38. Connected betweenthe junction of inductances l8 and 20 and the bus 30 are the capacitor40and the inductance 42. A serially connected capacitor 44 andinductance 46, are connected between the point A and the bus 30.

,A serially connected capacitor 48, and inductance 50, are connectedbetween the junction of inductances 16 and a bus 52. A seriallyconnected capacitor 54 and inductance 56, are connected between thejunction of inductances l2 and 16. A serially connected capacitor 58 andinductance 60, are connected between the junction of inductances 24 and26, and the bus 52. A serially connected capacitor 62 and inductance 64,are connected between the junction of inductances 26 and 28 and bus 52.

Capacitors 32, 36, 40, 44, 48, 54, 58 and 62 all have the value C.Inductors 34, 38, 42, 46, 50, 52, 60, 64 all have the value L. Thefunction of the eight capacitors designated C and numbered 32, 3 6, 40,44, 48, 54, 58 and 62 is to store energy provided by voltage sources 68and 70 for subsequent delivery to the load resistor l0. Theassociated-inductances designated L are unavoidable parasitic elements,recognized and integrated into the design in such a way as, to beharmless.

Between the busses 30 and 52, there are serially connected a currentlimiting resistor 66, a voltage source 68, another voltage source 79,and another current limiting resistor 72. Voltage sources 68 and 70 arepreferably equal. Between the point A and the junction between the twovoltage sources, there is connected a resistor 74. A normally openshorting switch is connected across the busses 30 and 52. Energy storedin the capacitors C is delivered to the load 10 when the switch isclosed. The resulting current has the waveform shown in FIG. 1A.

To operate the line shown in FIG. 1, a switch 76 is open until such timeas the capacitors become charged up. At that time, the switch is closed,whereby the shunt capacitors discharge into the series connectedinductances, which thereafter again discharge into the capacitors. Theoscillation which is thereby generated continues over a number of cyclesdetermined by the values and the number of sections selected in theconstruction of the line. The frequency of the oscillation is alsodetermined by the values of the components which have been selected.Those skilled in the art know how to select the inductance, capacitance,and resistance values required to produce the desired frequency ofoscillation in a desired number of cycles. It should be noted that theinductors L'are provided to accommodate any parasitic elements that maybe present.

The transmission line circuit shown in FIG. 1 is reentrant; therefore, asingle load represented by the resistor will absorb all of the powerstored in the line. The arrangement is such that the output is balancedto ground and no blocking capacitors are required. The arrangement showngenerates an even number of halfcycles. The waveform for the loadcurrent is represented in FIG. 1A. By altering the number of capacitorsemployed, that is, by substituting a load in place of one of the shuntcapacitors, an unbalanced output can be obtained, but at a lowerimpedance level.

FIGS. 2 and 3 respectively, show top and side views of a coaxial lineand disc structure which has distributed circuit components and whichrealizes the circuit arrangement shown in FIG. 1. It comprises a pair ofconductive discs respectively 80, 82, which are parallel with oneanother and spaced from one another. At the centers of the discs, attheir opposite faces, lumped protuberances or bosses, respectively 84,86 are provided. These bosses and the spacing therebetween constitute aspark gap switch.

To assist in triggering a discharge between the bosses provision may bemade at one or both of the bosses for a trigger electrode. By way ofexample, this can constitute a pin 85 extending into an opening 87 inthe boss 84. A voltage applied between the trigger electrode 85 and thedisc 80 from a trigger voltage source 89, which causes an arc dischargebetween the electrode and the edge of the opening 87, in the boss. Thisare triggers a discharge in the main gap between bosses 84 and 86.

Both top and bottom discs have openings, from which conductive tubesextend at right angles from the plane of the discs. In the top view,these tubes have reference numerals 88A, 90A, 92A and 94A, appliedthereto. In the side view of these tubes, only 88B and 94B may be seen.

A single conductor 96, extends into the space between the two discs,thereafter extends upward through the tube 88A and across and downwardthrough the tube 94A, through 94B, then across and upward through tube923 (not shown), upward through tube 92A, across to tube 90A throughwhich it proceeds downwardly through tube 90B (not shown), then across,upward through tube 888 and then out adjacent to the input lead. Theends of the conductor 96 are connected to a load 10. It should berecognized that the conductor and tubes form a series of coaxial linesconnected to the discs which form a spark gap switch.

A source of potential 98 is connected through the upper disc 80 througha charging resistor 100. A second and preferably equal source ofpotential 102 is connected to the upper disc through a charging resistor104. The lead 96 is connected to ground through a resistor 106.

In operation, the sources of charging potential are connected across thediscs. When the potential between the protuberances 84, 86 attains asufficient value, and with the assistance of the trigger electrode 85, adischarge is made to occur, which has the same effect as the shortingswitch 76 in FIG. 1. The inductances designated with the values L inFIG. 1, are distributed throughout the length of the zigzag circuitformed by the conductor 96. The capacitors are formed by the spacingbetween the conductor 96 and the tubes 88-94, A and B. Additional designflexibility is available by tapering the diameters of the conductorsthat make up the inductances and coaxial capacitance. At relatively highfrequencies, it may prove desirable to add tubular conductors thatshield the open inductive connections which bridge between the tubes,for example 94A, 88A.

By way of example, and not to serve as a limitation upon the invention,for operation at a frequency of 30 MHz, the spark gap section was madeabout 50 percent larger than that shown. The coaxial sections were madeof flexible coaxial cable each about 10 feet long. The

cable was of a type designated as RG8", now widely used for cable TV. Asecond model, was made and tested in which cable lengths were doubled(as well as stored energy) and the frequency of operation was lowered bythe same ratio.

In many situations, it is possible and desirable to enclose the entirestructure shown in FIGS. 2 and 3 in a sealed vessel containing a liquidof gaseous dielectric. Nitrogen at high pressure is an excellentdielectric that is favorable for high speed, high power spark switching.

FIGS. 4 and 5 show a variation of the structure shown in FIGS. 2 and 3,and differs in that a parallel strip transmission line is substitutedfor the coaxial arrangement shown in FIGS. 2 and 3. FIG. 4 is a top viewand FIG. 5 is a side view. The two discs and 82 in FIG. 5, are thickenedto essentially resemble two drums, respectively 110, 112. A plurality ofradial notches exemplified by notch 114 are formed in the periphery ofthe upper and lower drums, respectively 110, 112. Bosses, 118, areformed opposite one another at the centers of the drums 110, 112, andestablish a base therebetween which is the spark gap. A triggerelectrode (not shown) such as is shown in FIGS. 2 and 3, may also beemployed at one or both of the bosses to insure the occurrence of timelydischarges and also, since energy from the trigger generator is used toform the spark that makes the gap conductive, a larger fraction of theenergy stored in the transmission line is available for conversion intothe useful oscillatory wave delivered to the load.

Only fragments of the line, 122, which threads through the twenty slotsin the drums is shown in order to avoid confusion in the drawings. InFIG. 4, reference numeral 122A is applied to an illustration of acrosssection of the line. It may be seen that the line is broadened toextend approximately parallel to the surface of a slot. The geometry ofthe structure shown in FIGS. 4 and 5 is that of a parallel striptransmission line in place of the coaxial arrangement shown in FIGS. 2and 3. This geometry is especially attractive when, the number of cyclesto be generated is moderately large. I The structure shown in FIGS. 4and 5 has twenty slots and is therefore appropriate to form a pulse thatis ten cycles long. The length of the radial path from each line sectionto the switch can be made small compared to a wavelength withoutseriously reducing the stored energy.

The charging potential sources and the load are given the same referencenumerals, as in the previous drawings.

It should be noted, by way of example, and not as a limitation upon theinvention that the size of the embodiment of the invention shown inFIGS. 4 and 5 is correct for operation at a frequency near 1,200 MHz,corresponding to a wavelength of about inches.

There has accordingly been described and shown herein, a novel anduseful structure for a spark gap transmission line.

What is claimed is:

1. A spark gap pulse generator comprising:

a pair of spaced, conductive, circular structures which are opposite andcoaxial with one another,

a raised boss positioned at the center of each of said circularstructures and on the surface which is opposite the surface of the othercircular structure to establish a spark gap space therebetween,

each said circular structure having openings therethrough which aredistributed thereover and which are aligned with the openings in theother circular structure and v a conductor extending in between saidspaced circular structures and serially threading through all of thesaid openings therein.

2. A spark gap pulse generator as recited in claim 1 wherein each ofsaid spaced conductive circular, structure constitutes a disc, and g aconductive hollow tube extends away from each openings in said discs,

said conductor passing through the center of all of said tubes.

3. A spark gap pulse generator as recited in claim 1 wherein each ofsaid spaced conductive circular structures constitutes a drum,

said openings constitute elongated slots in the periphery of each saiddrum,

said conductor has a cross sectional area such that the surfacesubstantially parallels the surface of said elongated slots.

4. A spark pulse generator comprising:

a pair of spaced parallel conductive discs,

each disc having a raised boss mounted at the center thereof on thesurface opposite the other disc whereby a spark gap is established inthe space between the two bosses,

a plurality of aligned openings disposed over the surfaces of saiddiscs,

a hollow tube extending from each opening and right angles thereto, and

a conductor extending into the space between said disc, threadingthrough all of the tubes on both of said discs, and then extendingoutwardly from the space between said discs.

5. A spark gap pulse generator as recited in claim 4 wherein there isincluded:

a source of operating potential,

means for applying potential from said source to said discs,

a load, and

means for connecting the ends of said conductor extending from betweensaid two discs to said load.

6. A spark gap generator comprising:

a first and a second conductive drum spaced from one another and alignedwith one another,

each drum having a raised boss at the center of the surface which isopposite the surface of the other drum whereby a spark gap is defined bythe space between said two bosses,

each drum having radial notches in its periphery which are aligned withthe radial notches of the other drum, and

a conductor which extends from one end thereat into the space betweensaid two spaced drums and extends through all of the notchesof said twodrums, finally extending to its other end out through the space betweensaid two drums.

7. A spark gap generator as recited in claim 6 wherein said conductorhas a surface area which substantially parallels the surface area ofeach notch in said circular drum periphery.

8. A spark gap pulse generator as recited in claim 7 whereinthere isincluded a load which is connected to the two ends of said conductor,

a source of operating potential, and

means for applying potential from said source to said drums.

1. A spark gap pulse generator comprising: a pair of spaced, conductive,circular structures which are opposite and coaxial with one another, araised boss positioned at the center of each of said circular structuresand on the surface which is opposite the surface of the other circularstructure to establish a spark gap space therebetween, each saidcircular structure having openings therethrough which are distributedthereover and which are aligned with the openings in the other circularstructure, and a conductor extending in between said spaced circularstructures and serially threading through all of the said openingstherein.
 2. A spark gap pulse generator as recited in claim 1 whereineach of said spaced conductive circular, structure constitutes a disc,and a conductive hollow tube extends away from each openings in saiddiscs, said conductor passing through the center of all of said tubes.3. A spark gap pulse generator as recited in claim 1 wherein each ofsaid spaced conductive circular structures constitutes a drum, saidopenings constitute elongated slots in the periphery of each said drum,said conductor has a cross sectional area such that the surfacesubstantially parallels the surface of said elongated slots.
 4. A sparkpulse generator comprising: a pair of spaced parallel conductive discs,each disc having a raised boss mounted at the center thereof on thesurface opposite the other disc whereby a spark gap is established inthe space between the two bosses, a plurality of aligned openingsdisposed over the surfaces of said discs, a hollow tube extending fromeach opening and right angles thereto, and a conductor extending intothe space between said disc, threading through all of the tubes on bothof said discs, and then extending outwardly from the space between saiddiscs.
 5. A spark gap pulse generator as recited in claim 4 whereinthere is included: a source of operating potential, means for applyingpotential from said source to said discs, a load, and means forconnecting the ends of said conductor extending from between said twodiscs to said load.
 6. A spark gap generator comprising: a first and asecond conductive drum spaced from one another and aligned with oneanother, each drum having a raised boss at the center of the surfacewhich is opposite the surface of the other drum whereby a spark gap isdefined by the space between said two bosses, each drum having radialnotches in its periphery which are aligned with the radial notches ofthe other drum, and a conductor which extends from one end thereat intothe space between said two spaced drums and extends through all of thenotches of said two drums, finally extending to its other end outthrough the space between said two drums.
 7. A spark gap generator asrecited in claim 6 wherein said conductor has a surface area whichsubstantially parallels the surface area of each notch in said circulardrum periphery.
 8. A spark gap pulse generator as recited in claim 7wherein there is included a load which is connected to the two ends ofsaid conductor, a source of operating potential, and means for applyingpotential from said source to said drums.